Virulence, accumulation of acetyl-coenzyme A, and pectate lyase synthesis are controlled by PhoP-PhoQ two-component regulatory system responding to organic acids of Erwinia chrysanthemi 3937

Abstract

The PhoP-PhoQ two-components regulatory system is involved in the pathogenesis of animal, plant, and insect pathogenic bacteria in response to various environmental factors. To elucidate how this system contributes to the plant pathogenesis of Erwinia chrysanthemi 3937 (Ech 3937), marker-exchanged mutants of phoP and phoQ were constructed. Their role in the regulation of a major virulent factor, pectate lyase (Pel), in response to various organic acids was then tested. These mutants synthesized more Pel than did the wild type in the medium containing acetate or citrate as the sole source of carbon, but they synthesized less Pel than did the wild type in pyruvate or malate as the sole source of carbon. Synthesis of Pel did not differ in succinate, fumarate, or glycerol from the wild type. The phoP and phoQ mutants grown and resuspended in acetate or citrate also caused more maceration, and the wild type pretreated in pyruvate or malate caused more maceration than did the mutants. The level of intracellular acetyl-coenzyme A (acetyl-CoA) almost paralleled the synthesis of Pel in the wild type and in the mutants of the phoP and phoQ. These results suggested that acetyl-CoA may be involved in regulation of Pel synthesis through two-independent regulatory cascades via the PhoP-PhoQ system (in an opposite manner) in response to acetate/citrate and pyruvate/malate. However, ackA and pta genes, involved in the synthesis of acetyl-CoA in Escherichia coli, were not expressed as predicted on the basis of the level of acetyl-CoA. Thus there may be an additional regulation or pathway for the synthesis of acetyl-CoA in Ech 3937.